ent of the concentrations of minor components of air is routinely carried out. One of those components is nitrogen dioxide and its measurement is effected using luminol chemiluminescence. This procedure and equipment therefor is described by Schiff et al in U.S. Pat. No. 4,765,961 and reference may be had thereto for details thereof.
The measurement is rapid and sensitive. For example, the Luminox instrument, LMA-3, used in such measurements weighs only 7 kg and yet has a detection limit of 5 ppt (i.e. parts per trillion) with a time response of the order of 1 second.
Unfortunately, ozone interferes with the accuracy of the measurement for nitrogen dioxide. In some environments, this interference is not particularly significant, for example, in urban environments where there are relatively high concentrations of NO and hence NO.sub.2 from automobile traffic. However, in clean tropospheric background air, ozone interference becomes major.